1. Field
Example embodiments provide methods of reading memory cell data and nonvolatile memory devices, which may apply a low voltage to memory cells adjacent to a memory cell from which data may be read.
2. Description of the Related Art
Nonvolatile memory devices capable of electrically erasing and programming data may preserve data even when power is not supplied. Flash memory is an example of a nonvolatile memory device that stores data using charge storage. The memory cells of a flash memory may be, for example, cell transistors including a control gate, a charge storage layer, a source and a drain.
Flash memory controls the quantity of charges of the charge storage layers, to change data values written to the memory cells. Data of the cell transistor may be erased by applying a ground voltage to the control gate of the cell transistor and supplying a voltage higher than a power supply voltage to a semiconductor substrate and/or bulk. In the erase bias condition and/or state, a strong electric field may be formed between the charge storage layer and the bulk due to a large voltage difference between the charge storage layer and the bulk. The charges in the charge storage layer may be discharged to the bulk according to F-N (Fowler-Nordheim) tunneling and a threshold voltage of the erased cell transistor may therefore be decreased.
A cell transistor programming operation may be performed by, e.g. applying a voltage higher than a power supply voltage to the control gate of the cell transistor and applying a ground voltage to the drain and the bulk of the cell transistor. Under a bias condition, charges may be injected into the charge storage layer of the cell transistor by e.g. F-N tunneling, and the threshold voltage of the cell transistor may therefore be increased.
In an erase state the threshold voltage of the cell transistor is negative because the charge storage layer has negative charges and in a programmed state the threshold voltage of the cell transistor is higher than 0 because charges may be injected into the charge storage layer.